The objectives of this project are to trace the development of effortful control between the ages of 37 and 48 months, and to investigate children's verbal and physical self-regulatory strategies for control during this period. Effortful control is a major contributor to the development of conscience and the control of emotion for both children and adults. Three elements of executive control include: (1) conflict resolution, (2) the ability to monitor errors and (3) modulation of behavior to meet situational demands. Two proposed cross-sectional studies would provide a fine-grained analysis of the relationship among these components of executive control The first would use a modified Simon-Says task to induce conflict, and then examine the development of children's inhibitory control, strategies for control, and error detection. A second study would introduce randomly mixed conflict and non-conflict trials to examine the development of these functions and explore whether they function independently at each of the ages studied. Both studies would use the Children's Behavior Questionnaire (CBQ), a caregiver report of temperament, to examine the relationship between children's capacity for conflict resolution, error detection and strategy use in the laboratory, and caregiver report of children's levels of effortful control and negative affect in naturalistic settings.